The present invention pertains to pumping and filtration systems. More particularly, this invention relates to a pumping and filtration system for a corrosive chemical.
The invention finds particular application in the filtration of various fluids which are used in chemically etching semiconductor wafers. However, it should be appreciated that the invention also finds application in other environments in which it is necessary to filter a chemical, especially a corrosive fluid held at a high temperature.
Apparatus which is used to etch semiconductor wafers during their manufacture generally includes open-topped chemical baths which include a tank containing an etching solution and a weir basket held in the tank with the weir basket overflowing its top into the tank. The etching process takes place in the weir basket. The resultant waste products from the etching process float to the top of the solution or chemical in the weir basket and then flow into the tank. The chemical in the tank is pumped through a filter and the filtered chemical is subsequently returned to the weir basket for reuse. Such chemicals can be suitable conventional etching or cleaning fluids such as: sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, sodium hydroxide or potassium hydroxide.
Most filtration systems for such chemicals provide a filtration cartridge and a pump, for urging fluid through the cartridge, adjacent the tub. This type of system needs fittings and piping to interconnect the tub with the pump, the pump with the filter and the filter with the weir basket. Such fittings and piping need to be made of corrosion resistant plastic materials like PVDF or PTFE such as Teflon.RTM.. The problem with the use of such fittings an piping is the fact that the high temperature corrosive chemical softens the piping and fittings and may therefore cause leaks to occur at the joints of the fittings.
Another known system utilizes an integral submersible pump and filter unit positioned directly in the tub. However, this known unit utilizes a gas driven double-acting bellows pumping assembly which is complicated in its construction and is therefore expensive to manufacture. This unit also employs a multitude of valves which can be prone to failure. The bellows units utilized can also be prone to failure. Whenever any of these components fails, of course, the etching system is disabled and the entire unit needs to be removed and disassembled so that the faulty component can be replaced.
Accordingly, it has been considered desirable to develop a new and improved corrosive chemical filtration system which would overcome the foregoing difficulties and others while providing better and more advantageous overall results.